Grooved Dayem Nanobridges as Building Blocks of High-Performance YBa₂Cu₃O_7-δ SQUID Magnetometers

We present noise measurements performed on a YBa₂Cu₃O_7-δ nanoscale weak-link-based magnetometer consisting of a superconducting quantum interference device (SQUID) galvanically coupled to a 3.5 × 3.5 mm² pick-up loop, reaching white flux noise levels and magnetic noise levels as low as [Formula: see text] and 100 fT/[Formula: see text] at T = 77 K, respectively. The low noise is achieved by introducing grooved Dayem bridges (GDBs), a new concept of a weak link. A fabrication technique has been developed for the realization of nanoscale grooved bridges, which substitutes standard Dayem bridge weak links. The introduction of these novel key blocks reduces the parasitic inductance of the weak links and increases the differential resistance of the SQUIDs. This greatly improves the device performance, thus resulting in a reduction of the white noise.